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Metabolic
Engineering
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Metabolic
engineering for production of isoflavones in non-legume plants could
distribute the health benefits of these phytoestrogens to more
widely-consumed grains. Expression of a soybean isoflavone synthase
gene (IFS) in Arabidopsis plants was previously shown to result in
the synthesis and accumulation of the isoflavone genistein in leaf
and stem tissue.
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The
ability of the heterologous isoflavone synthase enzyme to interact
with the endogenous phenylpropanoid pathway, which provides its
substrate, was further investigated in several plant tissue systems.
In tissue that undergoes naturally enhanced synthesis of
anthocyanins, genistein production was enhanced.
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Induction
of the flavonoid/anthocyanin branch of the phenylpropanoid pathway
through stress treatment also enhanced genistein production. Both
previous effects were seen in dicot plant systems.
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In a
monocot cell system, introduced expression of a transcription factor
(CRC) that regulates genes of the anthocyanin pathway conferred the
ability to produce genistein in the presence of the isoflavone
synthase gene. However, in this case the intermediate accumulated to
high levels, indicating an inefficiency in its conversion.
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Introduction
of a third gene, chalcone reductase (CHR), provided the ability to
synthesize an additional substrate of isoflavone synthase resulting
in production of the isoflavone daidzein. The genistein produced in
the tobacco, Arabidopsis, and corn cells was present in conjugated
forms, indicating that endogenous enzymes were capable of
recognizing genistein as a substrate.
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Introduction
of seed-specific promoter driven IFS and CRC genes resulted in corn
plants where the isoflavone can be detected in the kernels.
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